X-ray image intensification and method



Aug. 25, 1953 W. C. WHITE X-RAY IMAGE INTENSIFICATION AND METHOD FiledOct. 10, 1952 Fig. I.

Viewin Side X-Ra s Inventor: William C. White,

His AttIOYnQH.

Patented Aug. 25. 1953 MET William 0. White, Schenectady, N. Y.,assignor to General Electric Company, a corporation of New YorkApplication October 10, 1952, Serial No. 314,069

' Claims. (01. 250-71 The present invention relates to the visualintensification of images produced by X-rays. It has been desired formany years to produce brighter X-ray images without operating at higherX-ray intensity. The patient being examined, the examining doctor, theX-ray technician and others dealing with X-ray examinations would beendangered by X-ray exposure if brighter images were to be obtained byincrease of X-ray intensity.

Heretofore visual images of an X-ray beam have been produced bythefluorescence of phosphors when bombarded by X-rays, for example, calciumtungstate.

It is the object of my invention to provide a method and means forproducing X-ray images or greater luminosity than is possible byfluorescence of phosphors while at the same time keeping down the X-rayintensity to a level that is not dangerous to those exposed to X-rayradiation.

In accordance with my invention visual images corresponding to aninvisible X-ray pattern are produced by an electroluminescent materialthrough the intermediary effect of a medium, the electrical impedance ofwhich is subject to variations by the passage of X-ray therethrough.

In the accompanying drawing Fig. 1 shows in perspective a framed X-rayintensifier and Fig. 2 is a cross-section taken on the lines 2-2 of Fig.l (in the direction of the arrows) and shows an assembly of elements forcarrying out my invention.

Referring to Fig. 2, a plate I of a light-transparent material, such asglass, is provided with a light-transparent electrically conductingcoating 2 on the inside surface of the glass. Glasses provided with alight-transparent conducting coating are commercially availableutilizing, for example, of conducting tin oxide. On this conducting film2 is deposited a thin layer or stratum 3 of electroluminescent phosphormaterial bonded by a resinous dielectric material, or otherwise appliedas a. thin layer over the surface of the conducting film 2.Electroluminescent phosphors are described in scientific literature andconsist of a material which becomes luminescent in an electric field.For example, U. S. patent application, Serial No. 245,696, Jerome S.Prener, filed September 8, 1951, which is assigned to the same assigneeas the present application, describes a phosphor of this type whichconsists of a fired mixture of about 60 parts zinc sulfide, 15 partszinc selenide and about 0.5 part copper. If zinc oxide is present as animpurity in such mixture it should be dissolved from the product bytreatment with acetic acid or other mild acid which may be followed bywashing with a dilute solution of an alkali cyanide. The resultingpowder is suspended in a dielectric material of high dielectricconstant. An electroluminescent phosphor is described in Mager U. S.Patent 2,566,349.

Contiguous with the stratum of electroluminescent material is amaterial, the electric impedence of which is subject to change due tothe X-rays passing therethrough, as exemplified by a stratum 4 ofclosely packed cadmium sul fide crystals. In the absence of X-rayexcitation the impedance of the stratum is higher than the impedance ofthe electroluminescent stratum Electric contact is made to the stratum 3at the exposed side (opposite contact between strata 3 and 4) with ayielding material which conforms with surface inequalities of theexposed side of stratum 4. For example, desired contact may be made witha very thin sheet 5 of aluminum backed by a sheet 6 of soft elastomer,such as rubber, so that by a gentle application of pressure, contactwill be madeover the extent of the stratum 4 even though such stratumshould have an uneven surface as will be the case if it consists ofparticles of varying size. The soft pressure-exerting sheet 6 is backedby a stiff sheet I of non-conducting material which is transparent toX-rays. It may consist of a suitable glass or a hard resin.

The described cooperating members are held in desired relation by aframe 8. Electrical contacts to the conducting coating 2 and to thebacking sheet of aluminum 5 are made respectively by the conductors 9and It]. To these conductors is connected a source of alternatingcurrent having a frequency and voltage suitable for theelectroluminescent material that is employed. Assuming a, source ofalternating current of suitable frequency (as, for example, 1 to 5kilocycles) to be connected to the conductors 9, l0 and X-rays impingingon the screen as indicated by the arrow, the impedance of the sulfidecrystals is lowered to a degree depending on the intensity of theX-rays.

When X-rays (as indicated by an arrow) strike the stratum 4 of cadmiumsulfide crystals the impedance of this material is lowered. Theresulting Variation of electric field will produce a correspondingvariable pattern of the light genrated by the electroluminescentmaterial. For example, a spot of high X-ray intensity will result in acorrespondingly bright spot of the electroluminescence layer 3. Anotherspot of low X-ray intensity which may be due to interception of X-raysby a dense object (for example, a bullet imbedded in tissue) will resultin little or no change of resistance in a corresponding adjacent spot ofthe layer 3. The result will be a shadow in the picture corresponding tothe outline of the bullet.

By means of the arrangement described, a luminous image will be producedin the layer of electroluminescent material 3 and visible through theglass I looking from the left side of Fig. 2',- as indicated. This imagewill be brighter than that obtained by the use of a Well-known materials that fiuoresce directly due to X-ray impingement. The crystalswhose conductivity is sensitive to X-rays introduce an element ofamplification. A brighter image thus results than could be obtained fromany known X-raiy-respon sive phosphor because the power to supply thisincrease comes from an independent electrical source. This introduces adegree of intensifica tion, the X-rays having what may be called atriggering effect on the electroluminescence of the material which isenergized from the indepedent source.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. The method of producing an intensified optically visible imagecorresponding to an optically invisible X-ray image comprising thefollowing steps: (a) arranging particlesof crystalline material whichwill change in electrical resistivity when irradiated with X-rays as apanel of desired spatial confi uration and closely adjacent to oneanother (b) arranging a second panel of an electroluminescent phosphorsubstantially coextensive with and in close proximity to said firstpanel particles setting up an electric field between said panels, and(d) subjecting said first-mentioned panel to X-ray radiation to beidentified, whereby resulting changes in electric field distributiontherein will produce an optically 'visible image in saidsecond-mentioned panel.

2. The method of reproducing, a visual image,

variations of an X-ray beam which consists in causing said variations toinitiate corresponding variations of electric impedance in a body ofcadmium sulfide crystals, impressing a high frequency electric field onsaid crystals, and exposing an electroluminescent material to theresulting pattern of electric field variations whereby a correspondingand intensified visual pattern is produced.

3. An X-ray image intensifier comprising the combination of a stratum ofmaterial, the electric impedance of which is subject to change by X-rayexcitation, a stratum of electroluminescent material, means forsupporting said respective strata in contiguous position, means forimpressing an electric field on said strata.

4. An X-ray screen comprising the combination of a layer of cadmiumsulfide, a contiguous layer of electroluminescent material, circuitmeans connecting said layers electrically in series, the impedance ofsaid cadmium sulfide layer in the absence of Xray excitation beinghigher than the impedance of said electroluminescent material, and meansfor impressing on said cadmium sulfide layer an X-ray beam having acontrasting' pattern of intensity capable of being reproduced visuallyby said electroluminescent layer.

5. X-ray image intensifier comprising a film of luminescent phosphor, atransparent support therefor, a layer of crystalline cadmium sulfideadjacent to and substantially coextensive with said phosphor, means formaking electrical contact respectively with said phosphor film and saidsulfide layer and means for impressing an electric field upon saidelectric contacts.

WILLIAM C. WHITE.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,523,132 Mason et al. Sept. 19, 1950 2,555,545 Hunter et a1.June 5, 1951 2,566,349 Mager Sept. 4, 1951

